Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., down hole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device down hole. To obtain such measurements, acoustic sources in sonic tools are sometimes used to determine the interaction between sonic waves and sub-surface formations.
Presently available sonic tools have a limited ability to generate strong low frequency flexural waves in formations. When conventional piezoelectric and electromagnetic sources are used, large amounts of power are typically required to generate significant acoustic energy. In addition, the fabrication of acoustic wave generation elements (e.g., piezoelectric crystals) that operate to produce a well-matched dipole source is difficult.